Introduction to Materials

1. ELECTRICAL ENGINEERING MATERIALS
(PROFESSIONAL ELECTIVE)

2. Course Learning Objectives:
• To impart the knowledge of conducting, dielectric, insulating and magnetic materials
and their applications.
• To impart the knowledge of superconducting materials and their applications
Module-1
Introduction to Electrical and Electronic Materials:
 Importance of materials
 Classification of electrical and electronic materials
 Scope of electrical and electronic materials
 Requirement of Engineering materials
 Operational requirements of electrical and
electronic materials
 Classification of solids on the basis of energy gap
 Products – working principle and materials
 Types of engineering materials
 Levels of material structure.
 Spintronics and Spintronic materials
 Ferromagnetic semiconductors
 Left handed materials.
Conductors:
 Conductor materials
 Factors affecting conductivity
 Thermal conductivity
 Heating effect of current
 Thermoelectric effect
 Seebeck effect
 Thomson effect
 Wiedemann – Franz law and
Lorentz
 Relation
 Problems.

3. Scope of Electrical and Electronic Materials
In Consumer Items
• Bulb filaments • Heaters • Remote control devices • Telephone • Domestic wiring
• Tape record • Switches • Iron press • Television • Invertors • Radio • Microwave ovens
In Electrical Engineering
• Contacts • Cables • Magnets • Alternators • Motors • Voltage Dividers • Conductors
• Dielectrics/Insulators • Piezo electrics • Transformers • Capacitors • Bus Bars, etc.
In Electronics
• Amplifiers • Integrated Circuits • Antenna • Broadcasting Systems • Printed Circuits
• Rectifiers • Filters • Regulators • Satellite • Photoconductive Cell • Transistors
• Modulators, etc.
In Robotics
• Sensors • Controls • Manipulators • Grippers • Actuators • Processors • Encoders
• Pendants, etc.
In Instrumentation
• Transducers • Signal generators • Microprocessors • Strain gauges • Recorders
• Cathode ray oscilloscopes • Thermistors • Energy meters, etc.

4. Classification of Electrical and Electronic Materials
Electrical engineering materials can be classified into following types:
1. Conductors
i. high voltage and low voltage conductors
ii. high temperature and low temperature conductors
iii. bared and insulated conductors
2. Semiconductors
i. intrinsic (or element) type ii. extrinsic (compound and alloy) type
• n type • p type
3. Dielectrics (or Insulators)
i. solid type ii. liquid type iii. gaseous type iv. ceramic type v. polymeric type vi.
fibrous
4. Superconductors
i. metallic type ii. ceramic type iii. ideal and hard types
iv. low and high temperature types v. magnetic and non-magnetic types
5. Magnetic materials
i. Diamagnetic ii. Paramagnetic iii. Ferromagnetic iv. Antiferromagnetic
v. ferrimagnetic

5. 6. Ferroelectrics
i. Zirconates ii. Hafnates iii. Titanates iv. PLZT
7. Piezoelectrics
i. Natural (as rochelle salt) ii. artificial (as tourmaline, metaniobate)
8. Perovskites (or mixed oxides)
9. Spinels, Garnets, and Magnetoplumbites
i. normal spinel (as ZnFe2O4) ii. inverse spinel (as magnetite) iii. metallic garnet
iv. rare earth garnet

6. Requirements of Engineering Materials
 Materials technology does not mean just knowing the physics and chemistry of
materials, their behavior and properties.
 It is also essential to know as to how a material can be suitably and
economically put to practical uses under wide range of conditions.
An electrical engineering material is used in one or all of the following areas.
• Machines (as motor, alternator, robots etc.)
• Structures (as transformer, cathode ray tube, antenna etc.)
• Devices (as strain gauge, integrated circuit, control switch, thermistor, bimetal gauge etc.)
• Instruments (as multimeter, transducers, thermocouples etc.)

7. Each material possesses several properties
 Some important properties
Electrical : - resistivity, conductivity, dielectric constant, dielectric strength, relaxation
time, loss angle, power factor.
Magnetic : - hysteresis, retentivity, permeability, susceptibility, coercive force,
reluctivity.
Electronic : - semi-conduction, drift , diffusion, concentration, energy gap, mobility,
carrier density, ionization energy, effective mass, density of state, rectifying action.
Optical :- reflection, refraction, transmission, fluorescence, lustre, luminescence.
Physical :- density, melting point, color, shape, size, finish, porosity.
Thermal :- expansion, conductivity, specific heat, thermal fatigue, thermal stress,
thermal shock, latent heat of fusion.

8. Operational Requirements of Electrical and Electronic Materials
Electrical materials have to satisfy widely varying needs of different operational
parameters. These parameters are voltage, current, temperature, frequency,
polarization, remanance, resistivity, emission etc.
• High and Low Voltage Applications
• High and Low Conduction Applications
• High and Low Temperature Services
• High and Low Frequency Services
• High and Low Resistivity Devices
• High and Low Emission Applications, Etc.

9. Conductors
All metals and alloys fall in the category of conductors. They are used in various
applications such as : -
• electricity transmission and distribution lines,
• electrical contacts viz. relays, brushes, switches etc., • resistors, and • heating
elements.
Gold is the best conductor of electricity followed by silver, copper and aluminum.
Keeping in view the cost factor, copper and aluminum are the natural choices
although silver is used for contacts in aircraft .
• Aluminium conductor reinforced with steel (ACSR) is an improved material for
transmission lines.
• Oxygen-free-high conductivity (OFHC) copper conductor is very suitable for low
temperature applications. It is a high

10. Characteristics of a Good Conductor
I. High Electrical And Thermal Conductivity,
Ii. High Melting Point,
Iii. Good Oxidation Resistance,
Iv. Low Cost,
V. Better Mechanical Properties.
Factors Affecting Conductivity (and Resistivity) of Metals
Resistance and resistivity.
The electrical resistance R of a conductor is related to its length l and area of cross-section a by
The electrical resistance and the resistivity of materials are influenced by
various factors such as given below.
1. Temperature,
2. Impurities, and
3. Plastic deformation.

11. 1. Resistance of a 200 meter long copper wire is 21 ohm. Its diameter is 0.44 mm.
Determine its specific resistance.

12. 1. Temperature Effect on Conductivity
• The electrical resistance of a conductor varies with its temperature.
• With a rise in temperature, the resistance of pure metals increases whereas it
decreases for semiconductors, insulators and electrolytes.
• The variation of resistance with temperature in a material can be expressed as
RT2 and RT1 are the resistances of the material at temperatures T2 and Tl respectively.
dT = T2 – T1 is the change in temperature
α is temperature coefficient of resistance of the material.

13. 2. Resistance of a conducting wire is 57.2 Ω at 70 `C and 50 Ω at
25 `C. Estimate its temperature coefficient of resistance.
Given are: R70 = Resistance at 70`C = 57.2 Ω, R25 = Resistance at 25 `C = 50 Ω

15. Thermal Conductivity
The transport of heat flux Q through a solid of cross-sectional area A is proportional
to the thermal gradient dT/dx, and is given by
Kt is a proportionality constant which is known as thermal
conductivity of the solid.
The negative sign indicates a drop in thermal gradient for
increasing length x.

16. Heating Effect of Current
• When an electric current flows through a metal (i.e. a conductor), the metal
becomes hot after some time.
• It is due to the collision of free electrons moving through the lattice of metals
in a random manner.
• During their movement (drift ), they collide with the atoms in the lattice of conducting
metals.
This results in generation of heat, and hence the phenomenon is termed as
‘heating effect of electric current’.
Joule’s Law of Electrical Heating
If a current of I ampere flows through a conductor of resistance R ohm for t second, then the
amount of work required (W.D.) to maintain the current flow will be given by

17. Heat equivalent of this work may be expressed as
J is mechanical equivalent of heat whose value is 4200
Applications of Heating Effect
• Electric furnace heating in metallurgical industry for melting of metals.
• Heating of electric kettle, heater, boiler, immersion heater etc.
• Heating of fi lament of incandescent lamp, arc lamp etc.
• Heating of d.c. locomotive for industrial hauling uses.
• In calorimetry.
• In fuses, which is used as protection device against flow of excessive current.
• In hot wire ammeter for measuring alternating current (a.c.).

18. Thermoelectric Effect (or Thermoelectricity)
The electrical energy can be converted into heat energy and the heating effect of
electric current is irreversible.
The heat energy can also be converted into electrical energy but this is a
reversible effect, and is known as thermoelectric effect.
 Applications of Thermoelectric Effect
Some important applications of thermoelectric effect are the following.
1. Temperature measurement of ovens and furnaces by means of a
thermocouple.
2. Temperature (radiation) measurement by thermopiles.
3. Detection of radiations by means of radio micrometer. A radio micrometer
is a combination of a thermocouple and a sensitive galvanometer.
4. Measuring a.c. and d.c. by thermo-milli ammeter

19. Seebeck Effect
Seebeck discovered that if the junctions of a closed circuit of two different metals is
maintained at different temperatures, then an electric current flows in the circuit.
The two-metal circuit system is referred to as ‘thermocouple’.
The flow of current implies that there acts an e.m.f. (electromotive force) in the circuit.
This e.m.f. is known as thermoelectric emf.
let us consider two different metals A and B in contact such that they form a junction
as shown in Fig (a) Now let the electron density in A > B
Then the electrons will diffuse
from positive A to negative B and a potential difference will be
created at the junctions H (hot) and C (cold).
This potential difference will allow the
flow of electrons from A to B until a state of equilibrium is
reached.

20. Seebeck e.m.f.
The thermoelectric e.m.f. of a thermocouple varies with a change in temperature
of the hot junction, or with temperature difference in the hot and cold junctions.
In general, the Seebeck e.m.f. is expressed by
Seebeck Voltage.
It is the difference in voltages of hot and cold junctions. Thus if VA and VB are the voltages at
hot and cold junctions, then

21. Thomson Effect
• This phenomenon refers to the absorption or evolution of heat due to flow
of current (electrons) in a single unequally heated conductor.
• Depending upon the absorption or evolution of heat in a conductor whose one end is
at higher temperature than the other, the hotter end will get heating effect and the
colder end will get cooling effect.
Wiedemann-Franz Law and Lorentz Relation
Statement. According to Wiedemann-Franz law, the electrical conductivity of
solids can be related to their thermal conductivity. It is because all the solids
conduct heat and electricity. Whereas the thermal conductivity in ionic, covalent
and molecular solids is primarily through lattice vibrations; the transport of
thermal energy in metals and alloys is mainly by free electrons.
Proof. To prove the above statement, we need to derive the expressions for
electrical and thermal conductivities.
We shall now derive the expression for thermal conductivity.